This patent application claims a priority based on a Japanese patent application, 2000-291623 filed on Sep. 26, 2000, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a distance information obtaining apparatus and a distance information obtaining method for obtaining information regarding a distance to an object. More particularly, the present invention relates to a distance information obtaining apparatus and a distance information obtaining method for obtaining the information of the distance to the object by detecting reflected light from the object irradiated with light.
2. Description of the Related Art
As a distance information obtaining method for obtaining a distance from a predetermined point to an object, a plurality of methods are proposed in which light is cast onto an object and the light reflected from the object is received so as to calculate the distance. These methods are generally classified into two groups, i.e., method based on triangulation and other methods.
In the methods based on the triangulation, a pattern of light is cast onto the object. From the position of the pattern of light, three-dimensional positional information is obtained based on the principle of the triangulation. In addition, there are a plurality of methods proposed other than the above, including a light cutting method, a grating projection method, a coded grading projection method, a colored grating projection method and Moire method. These methods are also based on the triangulation.
The methods that are not based on the triangulation include a time measuring method, a phase-difference measuring method, a method in which the distance to the object is calculated by using the distance between illumination light sources, and the like.
In the time measuring method, an ultra-short light pulse is emitted toward the object. The distance to the object is obtained by measuring the time until the reflected light is returned from the object.
In the phase-difference measuring method, light rapidly modulated is cast onto the object. The distance to the object is obtained by measuring a phase change when the reflected light is returned from the object.
As the method using the positional difference between the illumination light sources, exemplary methods are disclosed Japanese Patent Applications Laying-Open Nos. 61-155909, 62-46207 and 63-233312.
In the triangulation, it is necessary on its principle that a light-emitting position at which the light is emitted is away from a reflected-light receiving position at which the reflected light from the object is received. Thus, in a case of using a capturing device for use in a very narrow space, such as an endoscope, or a case where the object can be viewed only from limited positions, for example, excavation of ruins, offshore prospecting or researches by means of a planet landing research vessel, it is difficult to obtain the distance by the triangulation.
In addition, in the time measuring method, the speed of the light is very high. Thus, in order to improve resolution, it is necessary to provide an ultra-high speed optical device and electronics, increasing the cost of a measuring apparatus.
Moreover, in the method using the distance between the positions of the illumination light sources, the illumination light sources should be arranged away from each other. Thus, the size reduction of the measuring apparatus including the illumination light sources is difficult. Furthermore, since the positions of the illumination light sources are different from each other, an angle formed between a light ray and a surface of the object is varied in accordance with the position of the illumination light source. Thus, a measurement error is likely to occur.
Therefore, it is an object of the present invention to provide a distance information obtaining apparatus and a distance information obtaining method, which are capable of overcoming the above drawbacks accompanying the conventional art. The above and other objects can be achieved by combinations described in the independent claims. The dependent claims define further advantageous and exemplary combinations of the present invention.
According to the first aspect of the present invention, a distance information obtaining apparatus for obtaining information of a distance from a measurement-start point to an object, comprises: a light beam emitting unit operable to emit a light beam; a light beam scanning unit operable to scan the object with the light beam in such a manner that a center of scan is positioned on the measurement-start point; a reflected light detecting unit operable to detect reflected light from a point-of-interest on the object scanned with the light beam; a distance information calculating unit operable to calculate the distance from a scan velocity and a parameter related to an irradiation time of the object; and an information outputting unit operable to output the calculated distance.
The parameter may be based on a time from start to end of irradiation of the object with the light beam.
The light emitting unit may emit a plurality of light beams including at least a first light beam and a second light beam, the plurality of light beams traveling in directions approximately parallel to each other; and the distance information calculating unit may calculate, as the parameter, a time from detection of the reflected light of the first light beam to detection of the reflected light of the second light beam.
The distance information obtaining unit may calculate an integrated intensity of the reflected light at the point-of-interest as the parameter, and calculates the distance by using the integrated intensity thus calculated and a maximum intensity of the reflected light.
The light beam emitting unit may emit a fan-like light beam which diverges in a direction perpendicular to a scan direction, the fan-like light beam having a predetermined cross-sectional intensity distribution in the scan direction; the reflected light detecting unit may detect the reflected light from a region on the object, the region being scanned with the fan-like light beam; and the distance information calculating unit may calculate the distance at the point-of-interest within the region.
The light beam emitted by the light beam emitting unit may have a cross-sectional intensity distribution that is Gaussian distribution; and the distance information calculating unit may calculate the integrated intensity and the maximum intensity of the reflected light at the point-of-interest based on an integrated intensity and a maximum intensity of the light beam with which the point-of-interest is irradiated.
The light beam scanning unit may scan a plane perpendicular to a straight line passing through the measurement-start point and the point-of-interest at an approximately constant velocity.
The reflected light detecting unit may be provided on an optical axis of the light beam.
The reflected light unit may include a plurality of optical sensors operable to detect the reflected light from a plurality of points-of-interest; and the distance information obtaining unit may calculate, for each of the points-of-interest, the parameter for the reflected light detected by each of the plurality of optical sensors, and calculates the distance based on the parameter.
The distance information obtaining apparatus may further comprises a diffractive grating which diffracts the light beam emitting from the light beam emitting unit into a plurality of diffractive light beams.
In the distance information obtaining apparatus, the light beam scanning unit may scan the object with the plurality of diffractive light beams in direction of arraying the plurality of diffractive light beams.
In the distance information obtaining apparatus, the light beam scanning unit may scan the object with the plurality of diffractive light beams in perpendicular direction to arraying said plurality of diffractive light beams.
The reflected light detecting unit may be a capturing device operable to receive the reflected light from the object to capture an image of the object.
The distance information calculating unit may calculate the distance for at least one pixel of the image; and the information outputting unit may output a distribution of the distance.
The distance information calculating unit may calculate reflectivity from a maximum intensity of the reflected light at the point-of-interest and the distance, and the information outputting unit may output the reflectivity.
According to the second aspect of the present invention, a distance information obtaining method for obtaining a distance from a measurement-start point to an object, comprises: emitting a light beam; scanning the object with the light beam in such a manner that a center of scan is positioned on the measurement-start point; detecting reflected light from a point-of-interest on the object scanned with the light beam; calculating the distance from a scan velocity and a parameter related to an irradiation time of the object with the light beam; and outputting the calculated distance.
The parameter may be based on a time from start to end of irradiation of the object with the light beam.
A plurality of light beams may be emitted in the light beam emission step, the plurality of light beams including at least a first light beam and a second light beam and traveling in directions approximately parallel to each other. In this case, a time from detection of the reflected light of the first light beam to detection of the reflected light of the second light beam is calculated as the parameter in the distance calculation step.
The distance calculation step may include: calculating an integrated intensity of the reflected light at the point-of-interest; and calculating the distance by using a maximum intensity of the reflected light.
The summary of the invention does not necessarily describe all necessary features of the present invention. The present invention may also be a sub-combination of the features described above. The above and other features and advantages of the present invention will become more apparent from the following description of the embodiments taken in conjunction with the accompanying drawings.